The present invention generally relates to micro fluid dispensers using glass fibers. More specifically, the present invention relates to micro fluid dispensers using hollow glass fibers and piezoelectric material in ink print heads, as well as other applications.
A piezoelectric ink jet printer is a device that prints ink onto a variety of surfaces including paper. These printers use piezoelectric materials in various structures to force droplets of ink out of tiny nozzles. These drops shoot through the air to impact onto the paper or printing surface which passes below the print head. The ink rapidly dries on the paper. The accumulation of droplets from various nozzles on the print head forms characters on the paper surface. Usually, the paper moves underneath the printer to produces a continuous printing process. In low price consumer printers the printing mechanism is built into the printer. In higher cost industrial systems, such as those used for printing of signs or bar code labels onto boxes, the print head is actually a discrete unit from the rest of the printing system. Industrial print heads have many nozzles or channels to shoot out ink, typically from sixteen (16) to one-hundred-and-twenty-eight (128).
A piezoelectric is a material which will expand or contract when a voltage is applied to it. Conversely it can also generate a voltage or current when it is compressed or expanded. Typically, the piezoelectric material used in an ink jet print head is a ceramic based on the general chemical composition of Pb(Ti,Zr)O3. The piezoelectric ceramic is metallized with thin film electrodes so that a voltage can be applied to produce the desired mechanical expansion or contraction of the piezoelectric material. A number of companies manufacture piezoelectric ink jet print heads for industrial use. The manner in which the print head is constructed depends on the manufacturer. The two most common structures of print heads used in commercial printing applications involve cutting grooves or fingers into a piezoelectric ceramic plate. In the groove method, narrow rectangular grooves are cut into the piezoelectric plate at one end and extend almost to the other end of the plate. The grooves are narrow and deep. There are numerous grooves cut side by side, so that adjacent grooves share the same side walls. In a typical head there are one-hundred-and-twenty-eight (128) grooves. Thin film electrodes are deposited onto the walls of the grooves and then a cover is attached to the top of the piezoelectric plate to seal off the top of the grooves. A nozzle plate is attached on the end of the grooved plate where the grooves start. The nozzle plate is metal and has tiny holes machined in its surface spaced at distances to match the grooves in the grooved plate, so that one hole lines up with each groove. Ink is pumped through a manifold system located at the other end of the grooved plate filling all of the grooves with ink. During operation, a voltage pulse is applied across the groove walls, causing the walls to flex inward into the groove which squeezes ink out of the holes in the nozzle plate. By activating certain grooves in sequence droplets can be ejected toward the page to form characters on its surface.
The other design of ink jet print head uses the ceramic plate cut into fingers like a comb. A thin plate of piezoelectric ceramic is cut into a comb like structure with sixteen (16) or thirty-two (32) fingers. The ceramic is metallized with thin film electrodes before being diced into a comb, so that in the resultant structure, each finger has metal electrodes on both of its larger flat faces. The cuts extend almost the length of the ceramic. The solid end of the ceramic is then bonded down to a mounting block and the fingers extend forward into space. The fingers press against reservoirs of ink. These reservoirs have tiny nozzles on the side opposite to which the fingers press. The reservoirs are flexible so that when a voltage is applied across a given finger, that finger extends into the reservoir and forces a droplet from the nozzle on the opposite side of the reservoir. Again by activating the fingers in proper sequence, characters can be produced on the surface of the paper.
The two most common designs of industrial ink jet print heads described above suffer from many disadvantages. In the grooved plate design all of the grooves or ink channels are formed in the same piezoelectric ceramic plate so that if one channel fails it can""t be individually repaired and typically the whole plate is ruined. This leads to high yield losses during manufacturing and consequently higher costs. The end user also must buy a whole new head when it fails; instead of having it repaired, increasing his overall system use cost. In the groove design the channels can fail for several reasons. Pores in the ceramic material can cause leaks across the channels effectively short circuiting the device. Nozzles can easily clog from particle debris in the inks. This clogging is exacerbated by the structure of the device, with the wider grooves terminating in the small diameter holes in the nozzle plate. Larger particles can be trapped and build up in the space around the nozzle, eventually clogging the nozzle. Ink is in contact with electrodes of the channels so electrically conducting or chemically reactive inks can""t be used. The design is also not good for printing high viscosity inks or other substances such as glues. In short, the ink chemistry is severely constrained. The grooved plate print head manufacturing process is very difficult and it requires expensive equipment which also leads to high unit costs. The comb structure can""t be used to achieve a high number of channels above sixty-four (64) channels so it is only used in applications where print quality is not of major concern. It also suffers from the problem that if one channel fails the entire piezoelectric comb must be replaced.
A number of patents discuss using glass tubes for the ink delivery channels and/or nozzles in piezoelectric print heads. Some mention the use of piezoelectric element attached to the glass tube to eject ink. However, all of these use glass in the form of rigid tubes or capillaries and not flexible hollow fibers. Another group of patents describe making nozzle arrays for electrostatic printers out of glass tubes, capillaries, and fibers. In these patents the glass is cut into very short segments to form only the nozzle array or orifice plate and is not used for entire ink delivery pathway. Since these printers are electrostatic they do not use a piezoelectric to drive ink out of the glass tubes. Because of the potential advantages of using glass tubes in ink jet printers, there has been prior work in this area. However, none of this work includes the use of flexible hollow glass fibers. All patents using glass as the ink delivery system use rigid tubes or capillaries that are not flexible. Such an approach suffers from three major problems. One, the outer diameters of the tubes are large and prevent closely spacing them in a nozzle array. Therefore, fabricating a print head with a high dots-per-inch is very difficult. Second, because the tubes are rigid they can only be softened by heat and then permanently bent into angles necessary to fabricate a nozzle array which again makes the fabrication of a print head difficult. Third, because the tubes are rigid and not flexible they are prone to breakage during assembly and subsequent use, so the heads would be difficult to make and they would not be robust for an industrial environment.
It is an object of the present invention to provide micro fluid dispensers using glass fibers and piezoelectric devices.
It is another object of the present invention to provide micro fluid dispensers using glass fibers and piezoelectric devices to be used ink printing devices.
A micro fluid dispenser including reservoir, glass tube, hollow glass fiber, a piezoelectric element and a controller. The reservoir is to hold fluid to be dispensed. The glass tube has a first end, a second end and a tube body. The first end of the glass tube is connected to the reservoir to receive the fluid. There is a hollow glass fiber for each glass tube. The hollow glass fiber has a first end, a second end and a fiber body. The first end of the hollow glass fiber is connected to the second end of the glass tube to receive the fluid. The second end of the hollow glass fiber has an open tip to act as a nozzle to dispense the fluid. The piezoelectric element forces the fluid out of each of the open tip. The controller controls activation of the piezoelectric element.